1. Field of the Invention
The present invention relates to an apparatus and a method for determining variation over time of a medical parameter of a human being. The invention also relates to an implant for heart failure diagnostics comprising such an apparatus as well as a heart stimulator including such an implant to be used for controlling the stimulation.
2. Description of the Prior Art
The progress of medical parameters over time needs to be closely monitored to minimize patient pain, discomfort and hospitalization. Thus, as an example, for this purpose the progress of the cardiac function must be closely monitored over time as the cardiac failure condition changes.
An example of long term monitoring of a medical parameter is disclosed in U.S. Pat. No. 5,792,197. An implantable rate responsive pacemaker uses a physiological demand parameter to classify the patient's degree of congestive heart failure. The parameter is monitored for extended time periods to determine the levels for this parameter for different levels of physical activity of the patient.
Implantable sensors are most often incapable of sensing static information. The signal can be described as being dynamic. Due to this, it is of particular interest to be able to retrieve information for long term monitoring from dynamic sensor signals obtained from implanted sensors.